Rigid polyurethane and polyisocyanurate foams are manufactured by reacting and foaming a mixture of ingredients, in general an organic polyisocyanate with a polyol or mixture of polyols, in the presence of a volatile liquid blowing agent. The blowing agent is vaporized by the heat liberated during the reaction of isocyanate and polyol causing the polymerizing mixture of foam. This reaction and foaming process may be enhanced through the use of various additives such as amine or tin catalysts and surfactant materials that serve to control and adjust cell size and to stabilize the foam structure during formation. Foams made with blowing agents such as CCl.sub.3 F ("CFC-11") and CCl.sub.2 FCH.sub.3 ("HCFC-141b") offer excellent thermal insulation, due in part to the very low thermal conductivity of CFC-11 and HCFC-141b vapor, and are used widely in insulation applications.
Flexible polyurethane foams are generally open-cell foams manufactured using an excess of diisocyanate that reacts with water, also included as a raw material, producing gaseous carbon dioxide and causing foam expansion. The flexible foams are widely used as cushioning materials in items such as furniture, bedding, and automobile seats. Auxiliary physical blowing agents such as methylene chloride and/or CFC-11 are required in addition to the water/diisocyanate blowing mechanism in order to produce low density, soft grades of foam.
Many foam producers have converted from chlorofluorocarbon ("CFC") blowing agents, such as CFC-11, to environmentally safer hydrochlorofluorocarbon ("HCFC") agents and hydrocarbons. However, HCFCs, such as HCFC-141b, also have some propensity to deplete stratospheric ozone albeit significantly less than that of the CFCs.
Hydrocarbon agents, such as n-pentane, isopentane, and cyclopentane, do not deplete stratospheric ozone, but are not optimal agents because foams produced from these blowing agents lack the same degree of thermal insulation efficiency as foams made with the CFC or HCFC blowing agents. Further, the hydrocarbon blowing agents are extremely flammable. Because rigid polyurethane foams must comply with building code or other regulations, foams expanded with a blowing agent composed only of hydrocarbons often require addition of expensive flame retardant materials to meet the regulations. Finally, hydrocarbon blowing agents are classified as Volatile Organic Compounds and present environmental issues associated with photochemical smog production in the lower atmosphere.
In contrast to the foregoing blowing agents, hydrofluorocarbons ("HFCs") such as 1,1,1,3,3-pentafluoropropane ("HFC-245fa") do not deplete stratospheric ozone. This invention provides azeotrope-like compositions based on HFC-245fa and hydrocarbons for use as blowing agents for polyurethane-type foams.
Azeotropic blowing agents possess certain advantages such as more efficient blowing than the individual components, lower thermal conductivity or K-factor, and better compatibility with other foam raw materials. Additionally, azeotropic or azeotrope-like compositions are desirable because they do not fractionate upon boiling or evaporation. This behavior is especially important where one component of the blowing agent is very flammable and the other component is nonflammable because minimizing fractionation during a leak or accidental spill minimizes the risk of producing extremely flammable mixtures.
This invention provides azeotrope-like compositions that are environmentally safe substitutes for CFC and HCFC blowing agents, that have a reduced propensity for photochemical smog production, and that produce rigid and flexible polyurethane foams and polyisocyanurate foams with good properties. The invention also provides blowing agent compositions with reduced flammability hazards compared to hydrocarbon blowing agents.
Foams made with the blowing agent compositions of this invention exhibit improved properties, such as thermal insulation efficiency, improved solubility in foam raw materials, and foam dimensional stability, when compared to foams made with hydrocarbon blowing agents alone. Although the compositions of the invention contain a hydrocarbon, it is present as a minor component and, overall, the compositions are nonflammable.